1. Field of the Invention
The invention relates to porous polymers which are in powder form and contain N-vinylimidazole units, to a process for the preparation thereof by free-radical precipitation polymerization of N-vinylimidazoles, and to the use of the polymers as additive to phosphate-free and reduced phosphate detergents for inhibiting color transfer during the washing process.
2. Description of the Background
Polymers of 1-vinylimidazole are prepared, for example, by free-radical polymerization of 1-vinylimidazole in aqueous solution or in alcohols, cf. DE-A-2 814 287. To prepare high molecular weight or crosslinked polymers of 1-vinylimidazole it is possible to employ precipitation polymerization in benzene, cf. EP-A-0 162 388. The polymers result as crosslinked gels.
The use of copolymers of vinylimidazole and vinylpyrrolidone in detergent formulations of various composition is disclosed in EP-A-0 635 563 and EP-A-0 635 566. These copolymers are soluble in water. They are normally isolated by spray-drying aqueous solutions and are used in powder form to produce the detergents. In order to obtain the polymers from the aqueous solutions it is necessary to expend a large amount of energy to evaporate the water.
The older, not prior-published German Patent Application P 44 21 179.1 discloses the use of water-insoluble, crosslinked polymers which are in powder form and contain units of 1-vinylpyrrolidone and/or 1-vinylimidazoles as additive to detergents and cleaners to prevent color transfer during the washing process. The copolymers have a particle size of from 0.1 to 500 .mu.m.
The older, not prior-published DE Patent Application 19 519 328.5 discloses the preparation of crosslinked vinylimidazole/vinylpyrrolidone copolymers in surfactants and the use of the copolymer/surfactant mixtures obtainable in this way in detergents. The removal of the copolymers from the mixture with the surfactants, which are usually liquid or waxy, is very industrially complicated.
U.S. Pat. No. 3,689,439 discloses the preparation of crosslinked polyvinylpyrrolidones by polymerizing N-vinylpyrrolidone with suitable crosslinkers in the presence of free-radical polymerization initiators in aqueous solutions of electrolytes.
The electrolyte content is 5-80% by weight, based on water, and the electrolyte concentration must be high enough for phase separation to occur. This process results in relatively large, usually bead-like, hard particles with a smooth surface. Another disadvantage is that polymer deposits, which are difficult to remove, are formed on the inside wall of the vessel and on the stirrer.